This invention relates generally to a downhole tool and method providing for cooling an electrical portion of the tool. In a particular implementation the downhole tool is for testing pressure buildup and drawdown in a high temperature oil or gas well, and the method is for reducing temperature adjacent the electrical portion of the tool.
Electrical members, such as microprocessors and batteries, have been used or proposed for use in downhole tools that can perform various functions in an oil or gas well. For example, there is a downhole memory gauge, comprising a microprocessor, integrated circuit memory, and batteries, that can be lowered into a well to sense and record downhole pressures and temperatures. As another example, there have been disclosures of downhole tools used in drillstem tests and production tests during which valves in the downhole tools are controlled by electrical circuits in the downhole tools to open and close and thereby flow and shut-in the wells.
A limitation on the use of electrical components in a downhole tool is high temperature in the well. That is, electrical components are typically rated for reliable operation within a specified operating temperature range; outside such a range, unreliable or inefficient operation results. "High temperature" as used herein and in the claims encompasses temperatures outside such a predetermined operating temperature range. For example, particular electrical components might be rated for operation up to 350.degree. F. whereas a high temperature well might have temperatures up to 400.degree. F. or higher.
Although insulating or pre-cooling the electrical members before lowering them into the well might provide some protection against high temperatures in wells, any such protection will likely be only temporary and too short-lived if the tool is to be used for any extended period of time Thus, there is the need for a downhole tool and method by which extended protection against high downhole temperatures can be provided for one or more electrical members in the downhole tool. Preferably, such a tool and method should actively use a refrigeration cycle that is powered by pressure differentials in the well. Furthermore, such a tool and method should also preferably provide for extended use by recycling refrigerant through the refrigeration cycle. These needs particularly exist with regard to a downhole flow control tool such as a testing tool wherein the one or more electrical members preferably include a remotely responsive microprocessor adapted to operate a valve disposed in a flow path of a housing of the downhole tool so that a pressure buildup and drawdown test can be reliably performed in a high temperature well.